Duplicity v2.1.0 backups are failing with the error:
"... --gpg-options expected one argument".

The issue is that duplicity v2.1.0 began using the argparse Python
library and the parse_known_args function. This function
interprets the argument being passed, "--cipher-algo=AES256",
as an argument name (because of the leading '-') and not as an
argument value. Because of that it exits with an error and
reports that the --gpg-options arg is missing its value.

Adding an extra set of quotes around this string causes
parse_known_args to interpret the string as an argument
value.

…Duplicity 2.1.0

(Modified by JT.)

…sole to help debugging